FIG. 1 is a vertical cross-sectional view of a conventional electric motor driven scroll compressor which is disclosed as a "scroll compressor" in Japanese Patent Unexamined Publication No. 1-177481. The scroll compressor comprises: a compression unit 102 and a motor 103 mounted on the unit, the compression unit and the motor being provided inside of a sealed vessel 101; a body frame 105 of the compression unit 102 which frame sustains a driving shaft 104 driven by the motor 103; and a discharge chamber oil reservoir 106 provided between the body frame 105 and the motor 103. Oil in the discharge chamber oil reservoir 106 provided between the motor 103 and the body frame 105 is delivered to an annular groove 108 via an oil hole 107 formed in the body frame 105, and it is also supplied from the oil hole 107 to an eccentric bearing space 114 through a small gap of a sliding portion of a main rod bearing 109 and through an oil groove 113 formed in an eccentric bearing 112 for a swinging shaft 111 of a swinging scroll 110 provided on an end portion of the driving shaft 104. While the oil is passed through the small space of the sliding portion of the main rod bearing 109, its pressure is reduced to have a value of an intermediate pressure between the discharge pressure and the suction pressure. The oil in the eccentric bearing space 114 enters into an outer peripheral portion space 116 through an oil hole 115 formed in the swinging scroll 110, passes an oil hole 117 which is opened intermittently on the side of the swinging scroll 110, an injection groove 118 and two injection openings 119 having a small diameter, and flows into a compression chamber 120. As a result, it is the above-mentioned intermediate pressure which has been reduced in the small space of the sliding portion of the main rod bearing 109 that serves as a force to press the swinging scroll 110 against a fixed scroll 121.
However, the small space of the sliding portion has a large dispersion of manufacturing errors which makes it difficult to regulate the intermediate pressure with accuracy and induces a large fluctuation of the flow rate of the oil, so that the efficiency of the compressor may be affected by an amount of the oil which flows into the compression chamber 120. Besides, if a large amount of the oil flows into it, there is a risk that the compression chamber 120 may be broken by oil compression.